1. Field of the Invention
The present invention relates to a thin film transistor (TFT) and an electronic flat display device having the same, and, in particular, a thin film transistor and an electronic display device including nano particles in at least a channel.
2. Description of the Related Art
Organic electroluminescent display (OELD) devices can be classified as either passive matrix (PM), which uses a manual driving method, or active matrix (AM), which uses an active driving method.
In a PM OELD device, pixels are formed by anode electrodes and cathode electrodes arranged in columns and rows, respectively, whereby scanning signals are supplied to the cathodes from a row driving circuit. Only one row at a time, however, is selected from the plurality of cathode rows. Data signals are subsequently applied to the anodes from a column driving circuit to display an image.
In contrast, an AM OELD device controls individual pixels with control signals using a thin film transistor (TFT) and is widely used for displaying moving images since it is more suitable for processing a large number of signals.
A TFT of an AM flat display device includes a source region, a drain region, a semiconductor active layer having a channel region between the source and drain regions, a gate electrode insulated from the channel region, and source and drain electrodes.
The semiconductor active layer is conventionally formed of amorphous silicon or polysilicon. However, polysilicon has been more prevalent because amorphous silicon has poor electrical characteristics and low electrical reliability. The current mobility value of polysilicon can be as high as the hundreds of cm2/Vs, and polysilicon has good electrical characteristics, such as a low leakage current and high reliability.
However, a polysilicon is formed when crystallizing amorphous silicon by means of a crystallizing process that uses high temperatures exceeding 300° C.
Recently, flat display devices have become flexible so that they can be bent a certain amount when a predetermined tension is applied to secure a sufficient viewing angle. Thus, these flexible flat display devices have been used in portable products such as, for example, arm bands, purses, and notebook computers.
Nevertheless, it is difficult to obtain a flexible flat display device when using crystallized polysilicon TFTs formed by a method similar to the one described above. As a result, to form a flexible product, most of the display components, including the substrate, should be formed of a flexible material such as acryl, polyimide, polycarbonate, polyester, mylar, or plastic. But these materials, however, do not have high heat resistance.
Accordingly, for manufacturing polysilicon TFTs to be employed in a flexible flat display device, it is necessary to find a TFT structure that can be formed below a temperature at which the plastic can be processed.
A method for fabricating a TFT for use in a flexible product that includes a channel formed with a nano structure is described in Japanese Published Application 2004-048062.